This invention relates generally to marine mooring systems, and more specifically to multiple anchor systems wherein the anchors are self-emplacing. It has particular applicability to buoy systems wherein rapid and simple installation and maintenance of stable buoy position are required.
There are a significant and increasing number of requirements for easily deployable mooring systems for buoyant marine objects. It is frequently a further requirement that such mooring systems be capable of maintaining tight positional control of the buoyant objects under relatively severe environmental conditions, including adverse conditions of wind, waves and tidal currents. Examples of applications requiring such mooring systems include positional markers for marine navigation, fire fighting, diving operations, and identification of underwater points of interest; mooring apparatus for marine surveillance devices and instruments for obtaining hydrographic data and information on marine life; and anchoring devices for surface and subsurface pipe lines, storage tanks and marine vessels supporting underwater operations.
A large variety of methods and apparatus have been and/or are now employed for maintaining the positions of buoyant marine objects. One of the simplest systems involves tethering the buoyant object to a single underwater dead weight anchor by means of a chain or cable. Best positional control in such a system is achieved by maintaining the cable under substantial tension. This requires a massive anchor and a highly buoyant object. Thus, the system tends to be large and heavy for the function it performs, and is frequently not suitable for deployment from an aircraft or small vessel. In addition, even where substantial cable tension is maintained, positional control over the buoyant object is not particularly tight.
Much tighter positional control can be maintained by means of a mooring system which employs multiple spaced anchors. However, such systems generally suffer from the disadvantage of difficult and complex anchor emplacement procedures. This problem is aggravated if the system must be deployed under adverse wind, wave and current conditions. Multiple anchor system deployment procedures generally require at least two surface vessels. Typically the first of the plurality of anchors is lowered by one vessel while another vessel carries a second anchor to a spaced location at which time, the first vessel moves to yet another spaced location for emplacement of another anchor. In addition to requiring a substantial amount of marine equipment, there are problems in maintaining the anchor cables clear of one another while the system is being deployed.
Some of these disadvantages are overcome in mooring systems such as those disclosed in U.S. Pat. Nos. 3,295,153 and 3,611,974 issued to H. R. Dessau and R. G. Joppa et al. respectively. In each of these systems, a plurality of anchors are initially secured to guide rails on a floating structure. In the system disclosed in U.S Pat. No. 3,295,153, each anchor includes an element similar to a conventional fluked anchor attached to a torpedo-like cable carrier. During the deployment process the cable carriers are propelled by means of gas cartridges, and horizontally plane outwardly from a central flotation section. They simultaneously pay out cable secured to the central flotation section until their power is expended, after which they sink to the bottom.
In the system disclosed in U.S Pat. No. 3,611,974, guide rails on a surface vessel are oriented in the directions of desired anchor emplacement. When anchor deployment is desired, the anchors are accelerated along the guide rails by means of springs so as to impart a velocity sufficient to achieve stable gliding of the anchors. In both of these systems, the guide rail arrangements are cumbersome and require substantial space. In addition, special propulsion means is required to carry the anchors to their desired positions. The volume and weight of such systems makes them unsuitable for deployment from some aircraft and small marine vessels. In addition, the requirement for a special propulsion system is undesirable from the standpoint of manufacturing expense, maintenance, and reliability.
The applicant has overcome these problems by providing a multiple anchor mooring system wherein, prior to deployment, a plurality of gliding anchors are secured in a compact cluster. When deployment is desired, acceleration of the cluster to a velocity at least equal to the stable gliding velocity of the anchors may be provided by gravitational forces alone. The anchors are then automatically released to glide to their desired positions. Release of the anchors at a subsurface location results in accurate and predictable anchor emplacement wherein final anchor positioning is relatively unaffected by surface swells, currents and wind. Thus, an easily and accurately emplaceable multiple anchor mooring system of maximum simplicity and sufficient compactness for deployment from an aircraft or small surface vessel is achieved.